Metabolites of arachidonic acid play an important role as modulators or mediators of vascular tone and platelet aggregability. In this respect, the cyclooxygenase metabolites prostacyclin (PGI2) and thromboxane A2 (TxA2) seem to be of primary importance. However, arachidonic acid may also be metabolized by the lipoxygenase and epoxygenase pathway to hydroperoxy-, hydroxy-, epoxy- and dihydroxy-eicosatetraenoic acids (HPETE, HETE, EET and diHETE) as well as leukotrienes (LT). These compounds are also biologically active. The proposed studies will test the hypothesis that a metabolite or metabolites of arachidonic acid are involved in the regulation of platelet aggregability and vascular tone and that some cardiovascular drugs exert their effects by altering the synthesis or actions of these metabolites of arachidonic acid. The planned studies will focus on arachidonic acid metabolism and its regulation in vascular endothelial and smooth muscle cells. Human umbilical and pulmonary endothelial cells will be grown in tissue culture for these studies. Initially, these studies will identify the major metabolites of the cyclooxygenase, lipoxygenase and epoxygenase pathways (if existent). The physiological effects of the metabolites on platelet aggregability and vascular tone will be determined in vitro in human platelet rich plasma and isolated blood vessels. Assays will be developed for the metabolites that appear to be of physiological importance using radioimmunoassay or high pressure liquid chromatographic methods. These assays will be used to simultaneously measure products of the cyclooxygenase, epoxygenase and lipoxygenase pathways. The effects of various vasoactive substances will be tested for their ability to stimulate the synthesis of products by these pathways. Once compounds that stimulate the pathways are identified, their site of action will be identified, and the effect of antagonists determined. Detailed studies into the role of calcium, cyclic AMP or other factors in the cellular regulation of arachidonic acid metabolism by these pathways are planned.